Roving is produced by means of roving machines from (e.g. doubled) fiber slivers that are pretreated in most cases by drafting, and it serves as feed for the subsequent spinning process in which the individual fibers of the roving are spun into a fiber yarn, for example by means of a ring spinning machine. In order to give the roving a certain strength, it has proved to be useful to draft the sliver during the production of the roving by means of a drafting arrangement, which in most cases is part of the roving machine, and subsequently to provide it with a protective twist. The mentioned strength is important in order to prevent the roving from breaking during winding onto a bobbin or during feeding to the downstream spinning machine. However, the applied protective twist must only be strong enough that a cohesion of the individual fibers during the individual winding and unwinding processes and the adequate transport processes between the respective machine types is ensured. On the other hand, it has also to be ensured, despite the protective twist, that the roving can be further processed in a spinning machine—thus, the roving has still to be draftable.
In order to produce a corresponding roving, so-called flyers are primarily used; however, the delivery speed of the flyers is limited due to the occurring centrifugal forces. Thus, many different proposals have already been made to avoid the flyer or to replace it by an alternative machine type (see, for example, EP 0 375 242 A1, DE 32 37 989 C2).
In this connection it has already been proposed, among other things, to produce roving by means of air-jet spinning machines in which the protective twist is generated by means of air flows. The basic principle here is to guide a fiber sliver through a vortex chamber in which an air vortex is generated. The air vortex finally affects that a portion of the outer fibers are wound as so-called wrap fibers around the centrally extending fiber strand which, in turn, consists of core fibers which extend substantially parallel to each other.
However, as with the spinning of yarn, producing a roving usually also requires to piece the fiber sliver fed to the roving machine before the actual spinning process can be started. A corresponding piecing can be required, for example, upon switching on the spinning machine or after a breakage of the roving or the fiber sliver.
In spinning machines, it is prior art that the yarn end unwound from the bobbin is fed counter to the actual spinning direction through the spinning station and is connected to the fiber sliver delivered from the drafting arrangement. After passing the connecting station, the desired yarn is finally produced in the spinning station.
However, due to the above-mentioned properties of the produced roving, in particular the desired draftability thereof, a defined feeding of the roving back into or through the spinning station is only possible with great difficulties.